1. Field of the Invention
The present invention relates to a process for effectively separating isomers of disubstituted benzenes, which are useful as solvents, raw materials for chemical syntheses, etc., and to agents to be used for the separation. More particularly, it relates to a process for separating and recovering isomers of disubstituted benzenes which utilizes substituted cyclodextrins capable of including the isomers in a selective manner in accordance with their size and shape, and to substituted cyclodextrins to be used for the separation.
2. Prior Art
In general, isomers of disubstituted benzenes (i.e., o-, m- and p-isomers) are separated by means of distillation, based on the difference in their boiling points, or by means of crystallization, based on the difference in their melting points. However, since the boiling points of isomers of disubstituted benzenes are distributed within a relatively small range, separation based on distillation requires repeated superfractionation, which is not only time-consuming but requires much energy. On the other hand, separation based on crystallization suffers from the problem of eutectoid, and hence a mixture of the isomers could be separated in an effective manner only when it has a composition which can be substantially free from the problem.
Separation of isomers of disubstituted benzenes can also be effected by means of gas chromatography or high performance liquid chromatography. Although chromatography can be effective for analytical purposes, it is not suited for a commercial scale separation of the isomers. In another known technique, cyclodextrin or chemically modified cyclodextrins are used as an agent for separating isomers of benzene compounds (see, e.g., Japanese Patent Application (Laid Open) No. 42,825/77; "Process for Separating Isomers of Benzene Compounds"). In this process, isomers of benzene compounds are precipitated as inclusion complexes and subjected to a liquid-solid separating operation. However, inclusion complexes of cyclodextrins precipitate in the form of extremely fine precipitates which could be separated only through a highly troublesome solid-liquid separating operation.
It is therefore an object of the invention to provide a process for separating isomers of disubstituted benzenes in a highly selective manner.
It is another object of the invention to provide a process for separating isomers of disubstituted benzenes in an industrially advantageous manner.
It is a further object of the present invention to provide agents to be used for the separation of isomers of disubstituted benzenes.